JBL GT1281
Owner's Manual

Connecting Your Subwoofer to Your Ampli�er JBL GT Series subwoofers are available in three different con�gurations: single 4-ohm voice coil, single 8-ohm voice coil and dual 4-ohm voice coils. Depending on the ampli�er you are using, you may use either single- or dual-voice-coil subwoofers in singles or multiples to maximize the power available from your ampli�er. To achieve the maximum ampli�er output possible, you should design a speaker system that provides the lowest impedance that your ampli�er is rated to drive safely. When designing a subwoofer system, abide by the following rules: 1. Don�t mix different subwoofer or enclosure types in the same system (use all single-coil 4-ohm woofers, all singlecoil 8-ohm woofers, or all dual-coil woofers).

2. You may connect the coils of a dualvoice-coil woofer in series, but NEVER connect separate woofers in series. Because the ampli�er-damping factor (the ampli�er�s ability to control the motion of the woofer) is expressed as a ratio of terminal impedance (the sum of speaker impedance, wire resistance and the D.C. resistance of any crossover coil connected to the woofer) to ampli�er-output impedance, connecting woofers in series reduces the damping factor of the ampli�er to a value less than 1. This will result in poor transient response. 3. You must use both coils of a dualvoice-coil woofer either in series or in parallel. 4. Most ampli�ers deliver exactly the same amount of power bridged into a 4-ohm load as they do running a 2-ohm stereo load.

To design a subwoofer system that maximizes available ampli�er power, keep the following rules in mind: 1. The total system impedance of woofers in parallel = 1/(1/w1 + 1/w2 + 1/w3...) where w is the nominal impedance of the woofer. 2. The total system impedance of voice coils (or woofers) in series = w1 + w2 + w3... The diagrams below and at right show parallel and series speaker connections. Figure 1. Parallel connection

Figure 2. Series connection

03